1. Field of the Invention
The present invention relates to a mass analyzing apparatus. More particularly, the present invention relates to a mass analyzing apparatus capable of generating an ionization source by an RF power, without sample pretreatment at normal temperature and atmospheric pressure.
2. Description of the Related Art
In the conventional art, chemical compositions in samples (such as Chinese medicinal herbs) are analyzed by detection through liquid chromatography/mass spectrometer (LC/MS) or gas chromatography/mass spectrometer (GC/MS). The samples must be pretreated by being extracted with a solvent before being analyzed, so as to get signals.
FIG. 1 is a schematic view of an ionization source for a conventional direct analysis in real time (DART) as disclosed in U.S. Pat. No. 7,112,785.
Taking positive ions for example, the operational principle of the ionization source 1 includes: atoms of an inert gas (e.g., helium gas) that flow around the ionization source 1 are excited or ionized by a high voltage field at one atmosphere of pressure, as shown in Equation (1); next, the generated helium ions (He+) or the excited-state helium atoms (He*) impact with water molecules (H2O) in the atmosphere, to generate water ions (H2O+) and electrons (e−), as shown in Equation (2); then, water ions (H2O+) react with other water molecules (H2O), to generate hydrated ions (H3O+), as shown in Equation (3); finally, the hydrated ions and molecules (M) of a gas analyte from a sample perform an ion-molecule reaction, so as to generate molecular ions (MH+) of the analyte, as shown in Equation (4). Besides the above ionization process, the molecular ions of the analyte can also be formed by directly impacting the helium ions or excited state helium molecules with gas analyte, as shown in Equation (5).

The ionization source 1 has a metal needle 11 therein, and a DC high voltage is applied to the metal needle 11. Extremely high electric field intensity is generated due to the very small area of the top end of the metal needle 11, and the helium stream flows in through an inlet 12 behind the metal needle 11, to perform the reactions of Equations (1) to (3). As the ion-molecule reaction is merely suitable for gas molecules, the helium stream flows through a heating region 13, so that the temperature of the helium gas flowing out from the outlet 14 of the ionization source 1 is between 50° C. and 70° C. Once the hot gas stream containing helium gas, helium ions, and excited state helium molecules impacts the surface of the sample (usually, a solid), the chemicals on the surface of the sample are likely to be volatilized, so as to be reacted with the hydrated ions in the atmosphere to form analyte ions, i.e., perform the reactions of Equations (4) and (5). Then, the analyte ions enter a mass spectrometer for a mass analysis.
The ionization source 1 is characterized by its operation at an atmospheric pressure, so mass signals of the sample can be obtained without any sample treatment, which is very helpful for the object to be analyzed within a very short time or in situ in real time. The ionization source 1 can be used for analysis in the following situations: the detection of bombs in an airport and the rapid identification of air or water pollutants in environmental analysis. Additionally, the technique can also be used in situ to examine whether medicine is drugs, or to determine whether currency is real or fake by analyzing the ink chemicals.
The ionization source 1 is disadvantageous in that the operation environment is a high-voltage and high-temperature environment, which is very undesirable when the sample is a biomolecule, since the biomolecule is easily damaged in such an environment. Moreover, as the position where the plasma gas molecules are generated by the ionization source 1 is far away from the sample and the inlet of the mass spectrometer, after being dissociated, the excited state gas molecules are reduced to a basic state during the flight. Thus, the charge-carrying capacity of the sample molecules is reduced, which leads to poor detection efficiency. Additionally, the ionization source 1 needs a large gas stream, and therefore the operation cost is high.
Additionally, there is an inductively coupled plasma mass spectrometer (ICP MS), which is applied on ionizing metal atoms. However, in the ICP MS, in order to ionize the metal atoms, it is necessary to consume a large amount of energy, which is generally an AC voltage (1700 V) with an output power of 1200 W and an RF of 13.56 MHz. The temperature of the plasma generated at this condition is approximately between 6000° C. and 8000° C., and the used inert gas is argon gas (Ar), which cannot generate plasma discharge in an environment of high atmospheric pressure in order to generate ionized gas molecules, and thus cannot be applied in detecting biomolecules under an atmospheric pressure.
Therefore, it is necessary to provide a mass analyzing apparatus to solve the above problems.